The present invention relates generally to the fabrication of optical materials by electron beam radiation and more specifically to an apparatus and method for fabricating optical devices with a decreased birefringence while under tensile stress or a patterned birefringence under tensile stress utilizing electron beam radiation.
An optical material, which has two different indexes of refraction in two different directions, will divide an incident light beam into two light beams, an ordinary ray and an extraordinary ray. The ordinary ray and the extraordinary ray are in different polarization states but not cross-polarized. This optical property is called birefringence.
Halogenated optical materials are chemical compounds or chemical mixtures that contain halogen atoms, such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).
Halogenated optical materials typically have a single, uniform index of refraction. Halogenated optical materials also have a crystalline structure.
When halogenated optical materials are stretched or otherwise placed under tensile stress, the halogenated optical material is birefringent. The halogenated optical material under stress forms a high index of refraction area in one direction and a low index of refraction area in a second direction. The high index of refraction of the halogenated optical material under stress is higher than the normal index of refraction of the halogenated optical material not under stress. The low index of refraction of the halogenated optical material under stress is lower than the normal index of refraction of the halogenated optical material not under stress.
The difference in indexes of refraction between the high index of refraction and the low index of refraction in the halogenated optical material under stress is what causes the birefringence.
It is an object of the present invention to provide an electron beam irradiation method and apparatus to decrease and pattern the birefringence of halogenated optical materials under tensile stress.